Each year the number of battery powered electrical devices sold worldwide increases. Devices utilizing removable batteries include items of equipment such as flashlights, lanterns, radios, tape players and recorders, portable compact disc players, cameras, wall clocks, smoke detectors, hand and foot warmers, electronic games, and children's toys. In most cases, these devices are powered by throwaway primary batteries, presenting an ongoing expense to the user, and a disposal problem. Further, the widespread use of throwaway batteries wastes resources in terms of materials and energy required for their manufacture. Clearly, it would be of benefit to society if rechargeable batteries where more widely used.
Unfortunately, disadvantages inherent in the current practice discourage the widespread use of rechargeable batteries. Although charging units, both solar-powered and line-powered, are commercially available, a typical charging unit sells for the price of several sets of disposable batteries, making the cost of the initial investment a deterrent to many users. Moreover, the charging unit must be compatible with the batteries to be recharged. Since attempting to recharge a battery with an incompatible charging unit can pose a safety hazard, the user must be knowledgeable about battery-charger compatibilities. A substantial fraction of devices requiring removable batteries are children's toys. If small children are to recharge the batteries used in such toys, the issue of battery-charger compatibility and safety becomes extremely important. Also, since different types of batteries are frequently required in different electrical devices, the user may need to purchase several separate charging units of different types. Conventional chargers are limited to certain sizes and voltages of batteries, and to a certain number of batteries that can be recharged at one time. The user, therefore, must anticipate the types, sizes, voltages, and numbers of batteries to be used, when deciding which charging units to purchase. There is also the inconvenience to the user of keeping the appropriate charging unit ready to hand. This is particularly inconvenient when the device to be powered is highly portable, in which case the charging unit may be bulkier and heavier than the device to be powered.